If you need some info on girls in Tokyo check this out:
http://www.jgirls.com/pikup.htm
It's a pretty old page but still informative
Japan is awesome... I will be there again next month for two weeks. If you want kick ass night life you should go to Tokyo, for culture Kyoto is the best and if you have more time you should also go to Kyushu (one of the two southern islands).
Prices have gone down a bit in the last years. Regarding hotels... it's usually well worth it to go to a local travel agency in e.g. Tokyo as they offer some pretty good discounts. I once stayed a week in the Tokyo Hilton for about $100 a night. Just make sure there's no big convention at the same time.
If you need some more info hit me up on ICQ 5210719.